The present invention relates generally to archery bows. Specifically, the present invention relates to an improved archery bow and concave-shaped limbs therefor with improved efficiency, decreased limb weight, and increased strength.
Conventional archery bows typically have a stationary handle that does not bend and flexible limbs that do bend when the bow is drawn. This allows the bow to be held at the handle while the string is drawn back to deform the limbs. When the string is released, the limbs act like a spring in returning to their original undrawn position. The energy that was stored in the process of drawing the bow and deforming the limbs is used to accelerate three things when the string is releasedxe2x80x94the string, the arrow, and the limbs themselves. If the mass of the limbs can be reduced while still storing the same amount of energy, more of the stored energy can be transferred to the arrow and less wasted on accelerating the limbs forward. Another very important consideration is where this mass reduction occurs along the longitudinal axis of the limbs. That portion of the limbs that moves the farthest distance upon being released from the fully drawn position is even more significant. By removing mass from this outer portion of the limbs the benefits of reducing limb mass are maximized. In a well-made bow of conventional design up to 45% of the total stored force is unusable waste dissipated by the bow in restoring its limbs to the undrawn position. Such waste force can take the form of hand shock, vibration, and noise.
An archer can not materially change his/her draw length because of the fact that draw length is a function of physical size and arm length. So the only practical way to increase arrow speed is to increase the draw weight of the bow. Once again the archer is limited by his/her physical strength and corresponding ability to draw the bow. Raising the draw weight of a bow requires that the limbs be made thicker or wider or both. This has the unfortunate consequence of increasing the mass of the limbs. And as previously discussed, adding mass weight to the limbs reduces the efficiency of any given bow limb.
Conventional bows, either traditional or compound, employ limb geometries that have back and belly surfaces that are essentially perpendicular to the longitudinal axis of the bow and that are essentially parallel to one another. With this design concept, increasing the draw weight of a bow with conventional limb design requires that the limbs be made wider or thicker or both. Once again the effect of this is increased mass in the limbs which results in more energy waste upon the string being released.
Prior efforts to resolve these issues have been largely unsuccessful without adding weight to the bow structure, which also decreases bow efficiency. For example, compound bows add pulley systems and cams to the distal ends of the bow limbs. The addition of such apparatus to the limbs adds weight to the working bow structure, sometimes even doubling the weight of the bow. The addition of pulley systems and cams makes the bow easier to hold at full draw for aiming purposes, but adds weight. This added weight requires more energy to restore the limbs to the undrawn position. Further prior efforts have included the addition of springs and stabilizers to the bow structure. This dampens the effects of some of the waste force being dissipated in the form of hand shock, vibration, and noise, making the bow more comfortable for an archer to shoot. However, it does not decrease the overall amount of waste force being lost. Sometimes such additions even increase the waste force by adding to the overall weight of the working limb structure. These additional moving and working parts can also wear out and malfunction, and may need replacing, thereby making such additions potentially less advantageous
U.S. Pat. No. 4,122,821 to Mamo discloses an archery bow in which there are limbs outwardly extending from a center grip portion, and the cross-sections of the limbs at points along the longitudinal axis of the limbs are of predetermined curved configuration such that on drawing of the bow and decreasing of the radius of curvature of the longitudinal axis of the bow, there will occur at a predetermined rate, increase in the radii of transverse or cross-sectional curvature of the limbs.
Each bow limb structure has cross-sectional configurations that are curved in its transverse planes which are substantially perpendicular to its longitudinal axis. The configurations have predetermined dimensions of thickness and predetermined dimensions of extent of curvature which progressively vary at different sections of the limb structure. With increase of draw of the limb structures, the radius of longitudinal curvature significantly decreases while the radius of curvature of each configuration significantly increases in a progressive manner and at different rates at different sections.
Compound bows were originally developed because of an interest in reducing the amount of effort required to hold a bow at the fully drawn position so as to increase the ability of the archer to aim more carefully. Mamo sought to design a bow limb that would mimic the compound bow""s draw weight reduction at the fully drawn position.
U.S. Pat. No. 6,105,564 to Suppan discloses a bow with limbs which have a curved cross-section and whose longitudinal edges are oriented in a direction away from the bowstring, the cross-section of the limb (2, 3) extending with continuous curvature between the bow edges (2xe2x80x2, 3xe2x80x2), at least in the tensioned state.
As a result, there occurs a significant two-way movement during drawing of the bow, namely bending of the bow itself, on the one hand, and significant lateral spreading-apart of the longitudinal edges, on the other hand, such that the release movement proceeds in predetermined manner, namely by straightening of the bow itself with simultaneous forward movement of the edges relative to the bottom of the bow, thereby achieving faster restoration of the bow to its initial state, which leads to increased projection velocity for the bow.
U.S. Pat. No. 4,989,577 to Bixby discloses a power unit archery bow wherein a frame member is secured with respect to a first end of at least one limb member by a spring-actuated power unit. A bow string secured to a second distal end of the limb member is adapted to engage an arrow and to be drawn rearwardly by a user. Retraction of the bow string causes the limb member to rotate rearwardly, whereby the entire length of the limb member is utilized to load the spring member of the power unit.
Upon release of the bow string, the energy stored by the power unit spring is instantaneously released, being transmitted to the limb member to rotate the limb member to its original position so as to straighten the bow string and propel the arrow forward. Because the entire length of the limb member provides leverage to the power unit, the requisite pull force for the bow is greatly reduced.
These and other patents not specifically mentioned disclose attempts at enhancing performance of particular bows by adding various springs or frame work or power units or stabilizers or wheels and pulleys. None of these patents address the fundamental benefits of minimizing the overall mass of the working portion of a bow limb.
The present invention is provided to solve these and other problems.
The present invention is generally directed to using stiffening geometry to strengthen and therefore lighten the bow limb. The benefit of maintaining bow limb strength while significantly reducing limb mass is beneficial to traditional bows including recurves, reflex/deflex longbows, straight-limbed longbows, as well as to non-traditional bows consisting primarily of compound bows. Bows utilizing the present invention in their limb design will achieve equivalent levels of strength and stiffness with significantly less mass in the limbs when compared with a conventional bow. Bows utilizing the present invention will store just as much energy (all other things being equal) as bows utilizing conventional limb design. Draw/force curves for two otherwise similar bows, whether traditional or compound, will look essentially the same (See FIG. 10). However, because bows utilizing the present invention will have less mass in the limbs, more of the stored energy will be transmitted to the arrow.
Thus, in one embodiment, the present invention is directed to a bow with a handle having a longitudinal axis and first and second handle ends. The bow also has an upper limb and a lower limb extending generally in a direction along the longitudinal axis, each limb comprising first and second edges defining a limb width, a limb thickness, a proximal end, a distal end, and a working region between the proximal and distal ends of each limb. The first and second handle ends are attached to each limb at the respective proximal end of each limb. The proximal end of each limb has a proximal width and the distal end of each limb has a distal width. Each limb further has a concave surface extending generally between the first and second edges, each concave surface having an opening and first and second transition points located at opposing sides of the opening of the concave surface. A transverse width is defined by a distance between the transition points, wherein the transverse width is substantially unchanged when the bow is drawn to a full draw position as compared to when the bow is in an undrawn position. The transverse width can be the same as the limb width, and the first and second transition points can be located at the first and second edges, respectively.
In another embodiment, the present invention is directed to a limb for a bow having first and second edges defining a limb width, a limb thickness, a proximal end, a distal end, and a working region between the proximal and distal ends of the limb, wherein the proximal end of the limb has a proximal width and the distal end of the limb has a distal width. The limb further has a concave surface extending generally between the first and second edges, the concave surface having an opening and first and second transition points located at opposing sides of the opening of the concave surface. A transverse width is defined by a distance between the transition points, wherein the transverse width is substantially unchanged when the bow is drawn to a full draw position as compared to when the bow is in an undrawn position.
In an additional embodiment, the present invention is directed to a bow having a handle with a longitudinal axis and first and second handle ends. The bow also has an upper limb and a lower limb extending generally in a direction along the longitudinal axis. Each limb has first and second edges defining a limb width, a limb thickness, a proximal end, a distal end, and a working region between the proximal and distal ends of each limb. The first and second handle ends are attached to each limb at the respective proximal end of each limb, wherein the proximal end of each limb has a proximal width and the distal end of each limb has a distal width. Each limb further has a concave surface extending generally between the first and second edges, each concave surface having an opening and first and second transition points located at opposing sides of the opening of the concave surface. A transverse width is defined by a distance between the transition points. The bow further has a draw force that is required to draw the bow from an undrawn position to a draw length, wherein the draw force required to draw the bow increases as the draw length increases within the vicinity of a full draw position and beyond the full draw position.
In yet a further embodiment, the present invention is directed to a limb for a bow having first and second edges defining a limb width, a limb thickness, a proximal end, a distal end, and a working region between the proximal and distal ends of the limb, wherein the proximal end of the limb has a proximal width and the distal end of the limb has a distal width. The limb further has a concave surface extending generally between the first and second edges, the concave surface having an opening and first and second transition points located at opposing sides of the opening of the concave surface. A transverse width is defined by a distance between the transition points. The transverse width can be the same as the limb width, and the first and second transition points can be located at the first and second edges, respectively. There is also a draw force that is required to draw the bow from an undrawn position to a draw length, wherein the draw force required to draw the bow increases as the draw length increases within the vicinity of a full draw position and beyond the full draw position.